Many vehicles provide passive entry and/or remote vehicle starting systems. These systems allow the user to carry a key fob with one or more labeled buttons, and to press a particular button for locking or unlocking one or more vehicle doors, unlocking a hatch or trunk, enabling and disabling anti-theft systems, sounding an alarm, starting the vehicle, etc. The key fob device includes RF communications circuitry and a small battery, and is typically programmed with a unique ID code. The vehicle includes a passive system which communicates with the key fob and verifies that the ID code in the fob is authorized for activating one or more vehicle functions. Some systems also include sensors to detect whether the key fob is located in the vehicle interior or in the vicinity of the vehicle, and the system can alert the user of undesirable events such as attempting to lock the doors while the key fob is inside the vehicle.
Many modern vehicles are also equipped with interfaces for accommodating and interacting with personal communication devices, such as cell phones, PDAs, tablets, laptop computers, portable GPS devices, etc. These portable devices are typically battery-powered, and frequently require recharging. Accordingly, vehicles are often used to charge battery-powered devices, such as by connection of a charger to the vehicle battery through a cigarette lighter adapter. More recently, non-contacting charging stations have been developed in which the battery-powered device includes an inductor coil that can operate as a transformer secondary winding when placed near an energized primary coil, with the charging station including a primary coil and a power supply. When the battery-powered device is positioned on or near the charging station, the primary and secondary coils form a transfer to transfer charging power from the charging station to the battery-powered device.
These inductive charging stations advantageously allow charging of a variety of different user devices without requiring the user to physically connect the device to the charging station by cables or wires. However, inductive charging stations can cause electromagnetic interference (EMI) or radio frequency interference (RFI) at one or several frequencies that could interfere with passive entry/starting system communications. Such interference could prohibit the user from being able to start/stop the vehicle engine and/or cause a failure of the system to warn the driver of an unwanted event like locking the key fob inside the car, etc. Thus, there is a need for improved motor vehicle systems and inductive charging techniques by which battery-powered devices can be inductively charge in a motor vehicle.